Revert "Create a base class for clients"

This reverts commit a51bcd3.

Author: lidizheng

gapic/templates/%namespace/%name_%version/%sub/services/%service/async_client.py.j2

@@ -22,9 +22,9 @@ from google.oauth2 import service_account              # type: ignore
 {% endfilter %}
 from .transports.base import {{ service.name }}Transport
 from .transports.grpc_asyncio import {{ service.name }}GrpcAsyncIOTransport
-from .base_client import {{ service.name }}BaseClient, {{ service.name }}BaseClientMeta
 
-class {{ service.async_client_name }}Meta({{ service.name }}BaseClientMeta):
+
+class {{ service.async_client_name }}Meta(type):
     """Metaclass for the {{ service.name }} client.
 
     This provides class-level methods for building and retrieving
@@ -55,13 +55,149 @@ class {{ service.async_client_name }}Meta({{ service.name }}BaseClientMeta):
         return next(iter(cls._transport_registry.values()))
 
 
-class {{ service.async_client_name }}({{ service.name }}BaseClient, metaclass={{ service.async_client_name }}Meta):
+class {{ service.async_client_name }}(metaclass={{ service.async_client_name }}Meta):
     """{{ service.meta.doc|rst(width=72, indent=4) }}"""
 
+    @staticmethod
+    def _get_default_mtls_endpoint(api_endpoint):
+        """Convert api endpoint to mTLS endpoint.
+        Convert "*.sandbox.googleapis.com" and "*.googleapis.com" to
+        "*.mtls.sandbox.googleapis.com" and "*.mtls.googleapis.com" respectively.
+        Args:
+            api_endpoint (Optional[str]): the api endpoint to convert.
+        Returns:
+            str: converted mTLS api endpoint.
+        """
+        if not api_endpoint:
+            return api_endpoint
+
+        mtls_endpoint_re = re.compile(
+            r"(?P<name>[^.]+)(?P<mtls>\.mtls)?(?P<sandbox>\.sandbox)?(?P<googledomain>\.googleapis\.com)?"
+        )
+
+        m = mtls_endpoint_re.match(api_endpoint)
+        name, mtls, sandbox, googledomain = m.groups()
+        if mtls or not googledomain:
+            return api_endpoint
+
+        if sandbox:
+            return api_endpoint.replace(
+                "sandbox.googleapis.com", "mtls.sandbox.googleapis.com"
+            )
+
+        return api_endpoint.replace(".googleapis.com", ".mtls.googleapis.com")
+
+    DEFAULT_ENDPOINT = {% if service.host %}'{{ service.host }}'{% else %}None{% endif %}
+    DEFAULT_MTLS_ENDPOINT = _get_default_mtls_endpoint.__func__(  # type: ignore
+        DEFAULT_ENDPOINT
+    )
+    DEFAULT_MTLS_TRANSPORT = {{ service.grpc_asyncio_transport_name }}
+
     @classmethod
-    def _default_mtls_transport(cls) -> str:
-        """Returns the default MTLS transport name."""
-        return "grpc_asyncio"
+    def from_service_account_file(cls, filename: str, *args, **kwargs):
+        """Creates an instance of this client using the provided credentials
+        file.
+
+        Args:
+            filename (str): The path to the service account private key json
+                file.
+            args: Additional arguments to pass to the constructor.
+            kwargs: Additional arguments to pass to the constructor.
+
+        Returns:
+            {@api.name}: The constructed client.
+        """
+        credentials = service_account.Credentials.from_service_account_file(
+            filename)
+        kwargs['credentials'] = credentials
+        return cls(*args, **kwargs)
+
+    from_service_account_json = from_service_account_file
+
+
+    {% for message in service.resource_messages -%}
+    @staticmethod
+    def {{ message.resource_type|snake_case }}_path({% for arg in message.resource_path_args %}{{ arg }}: str,{% endfor %}) -> str:
+        """Return a fully-qualified {{ message.resource_type|snake_case }} string."""
+        return "{{ message.resource_path }}".format({% for arg in message.resource_path_args %}{{ arg }}={{ arg }}, {% endfor %})
+
+    {% endfor %}
+
+    def __init__(self, *,
+            credentials: credentials.Credentials = None,
+            transport: Union[str, {{ service.name }}Transport] = None,
+            client_options: ClientOptions = None,
+            ) -> None:
+        """Instantiate the {{ (service.client_name|snake_case).replace('_', ' ') }}.
+
+        Args:
+            credentials (Optional[google.auth.credentials.Credentials]): The
+                authorization credentials to attach to requests. These
+                credentials identify the application to the service; if none
+                are specified, the client will attempt to ascertain the
+                credentials from the environment.
+            transport (Union[str, ~.{{ service.name }}Transport]): The
+                transport to use. If set to None, a transport is chosen
+                automatically.
+            client_options (ClientOptions): Custom options for the client.
+                (1) The ``api_endpoint`` property can be used to override the
+                default endpoint provided by the client.
+                (2) If ``transport`` argument is None, ``client_options`` can be
+                used to create a mutual TLS transport. If ``client_cert_source``
+                is provided, mutual TLS transport will be created with the given
+                ``api_endpoint`` or the default mTLS endpoint, and the client
+                SSL credentials obtained from ``client_cert_source``.
+
+        Raises:
+            google.auth.exceptions.MutualTlsChannelError: If mutual TLS transport
+                creation failed for any reason.
+        """
+        if isinstance(client_options, dict):
+            client_options = ClientOptions.from_dict(client_options)
+
+        # Save or instantiate the transport.
+        # Ordinarily, we provide the transport, but allowing a custom transport
+        # instance provides an extensibility point for unusual situations.
+        if isinstance(transport, {{ service.name }}Transport):
+            # transport is a {{ service.name }}Transport instance.
+            if credentials:
+                raise ValueError('When providing a transport instance, '
+                                 'provide its credentials directly.')
+            self._transport = transport
+        elif client_options is None or (
+            client_options.api_endpoint == None
+            and client_options.client_cert_source is None
+        ):
+            # Don't trigger mTLS if we get an empty ClientOptions.
+            Transport = type(self).get_transport_class(transport)
+            self._transport = Transport(
+                credentials=credentials, host=self.DEFAULT_ENDPOINT
+            )
+        else:
+            # We have a non-empty ClientOptions. If client_cert_source is
+            # provided, trigger mTLS with user provided endpoint or the default
+            # mTLS endpoint.
+            if client_options.client_cert_source:
+                api_mtls_endpoint = (
+                    client_options.api_endpoint
+                    if client_options.api_endpoint
+                    else self.DEFAULT_MTLS_ENDPOINT
+                )
+            else:
+                api_mtls_endpoint = None
+
+            api_endpoint = (
+                client_options.api_endpoint
+                if client_options.api_endpoint
+                else self.DEFAULT_ENDPOINT
+            )
+
+            self._transport = self.DEFAULT_MTLS_TRANSPORT(
+                credentials=credentials,
+                host=api_endpoint,
+                api_mtls_endpoint=api_mtls_endpoint,
+                client_cert_source=client_options.client_cert_source,
+            )
 
     {% for method in service.methods.values() -%}
     {% if not method.server_streaming %}async {% endif -%}def {{ method.name|snake_case }}(self,
@@ -176,7 +312,7 @@ class {{ service.async_client_name }}({{ service.name }}BaseClient, metaclass={{
             ),
             {%- endif %}
             default_timeout={{ method.timeout }},
-            client_info=self._client_info,
+            client_info=_client_info,
         )
         {%- if method.field_headers %}
 
@@ -231,6 +367,16 @@ class {{ service.async_client_name }}({{ service.name }}BaseClient, metaclass={{
     {% endfor %}
 
 
+try:
+    _client_info = gapic_v1.client_info.ClientInfo(
+        gapic_version=pkg_resources.get_distribution(
+            '{{ api.naming.warehouse_package_name }}',
+        ).version,
+    )
+except pkg_resources.DistributionNotFound:
+    _client_info = gapic_v1.client_info.ClientInfo()
+
+
 __all__ = (
     '{{ service.async_client_name }}',
 )